1. Field of the Invention
This invention relates to colored glass and particularly relates to the production of metal oxide coated glass for solar energy control.
2. Description of the Prior Art
In the preparation of metal or metal oxide films on large substrates there has been a significant body of teaching relating to the preparation of such coatings by pyrolytic techniques. The art of pyrolytic coating of glass is characterized by the following patents:
U.S. Pat. No. 3,081,200 to Tompkins and U.S. Pat. No. 3,410,710 to Mochel teach that metal oxide coatings may be applied to refractory materials by contacting the refractory, while hot, with compositions containing metal diketonates.
U.S. Pat. No. 3,652,246 to Michelotti and Henry and U.S. Pat. No. 3,660,061 to Donley, Rieser and Wagner teach the application of metal oxide coating on a continuous ribbon of float glass having dissolved tin in its surface regions.
These described patents provide a recent history of the development of the art of coating glass with metal oxides by pyrolysis. As each improvement in turn has been implemented, coatings of improved quality both as to appearance and durability have been obtained. Metal oxides of a variety of metals may be deposited on glass by techniques known in the art. Metal oxides deposited in the manner taught by Donley, Rieser and Wagner are found to adhere to glass with sufficient tenacity to provide coatings capable of withstanding prolonged atmospheric attack in exposed architectural applications. However, accelerated weathering tests have shown that, depending upon the particular metal oxide or combinations of metal oxides present in the coating compositions, some of the metal oxide coatings will fail after prolonged exposure to corrosive atmospheres, such as those containing acidic pollutants or salt water. Improved durability of all useful metal oxide coatings on glass has been considered a desirable objective. Also, since the composition changes necessary to produce differing color effects yield films of differing durability, it has been an objective to increase the range of colors that may be achieved with a given composition so that a variety of colors are available for use without the necessity of prolonged durability testing for each new colored coating prior to its use.
In U.S. Pat. No. 3,467,508 Loukes et al. teach a method of making colored glass articles. By modifying the surface of the glass substrate with selected metals, other than the tin which is normally present at the surface of float formed soda-lime-silica glass, it is possible to provide the glass with stained surface layers of various desired colors. Unfortunately, such metal modified glass surfaces, characterized in the art as "ion-exchanged" surfaces, are relatively soft and are easily damaged by mild abrasion. Therefore, it is practical to limit the use of such articles to interior applications or double glazed windows where durability is not as critical as for exposed exterior surfaces.
Coatings made by the described pyrolytic techniques and stains made by the described "ion-exchange" technique yield colored articles wherein the colors depend on the composition of the coloring medium. In order to obtain different colors it is necessary to modify the components of the coloring medium. A preferable result would follow from the utilization of the same basic composition to provide a variety of colors.
It is known that selectively reflecting and transmitting interference filters can be produced by using materials of widely different indices of refraction in multiple-layer films of controlled thicknesses. Such multiple-layer films have been designed to effectively filter out all but narrow bands of light having the desired dominant wavelengths. These prior art multiple-layer films have usually been made by vacuum evaporation deposition techniques. Such evaporation deposition methods are not readily adaptable to continuously coating large sheets of glass for use as viewing enclosures in architectural applications. On the other hand, pyrolytic techniques normally used to continuously coat large sheets of glass are not particularly suited to making multiple-layer films. Reheating would generally be required between coating steps and this can easily cause distortion in both the glass and the previously applied layers of the final film.